1. Field of the Invention
The present invention relates to information for correction of stored or calculated values and the transfer thereof.
2. Description of Related Art
Ease and accuracy of position determination has increased significantly since the development of positioning technologies such as global positioning satellite (xe2x80x98GPSxe2x80x99) systems. One example of a system of positioning satellites is the NAVSTAR GPS system (as described in Global Positioning System Standard Positioning Service Signal Specification, 2nd edition, Jun. 2, 1995, United States Coast Guard Navigation Center, Alexandria, Va.); another example is the GLONASS GPS system maintained by the Russian Republic. GPS receivers are currently available for use in aircraft, ships, ground vehicles, and for hand carrying by individuals.
The NAVSTAR GPS system currently comprises twenty-four satellites or xe2x80x98space vehiclesxe2x80x99 (xe2x80x98SVsxe2x80x99) that orbit the earth in six orbital planes (four satellites in each plane). The SV orbits repeat substantially the same ground track as the earth turns beneath them each day. The orbital planes are equally spaced and inclined with respect to the equatorial plane, thus ensuring that a line-of-sight path exists to at least five SVs from any (unobstructed) point on the earth.
Ground-based monitor stations measure signals from the SVs and incorporate these measurements into orbital models for each satellite. Navigation data and SV clock corrections are computed for each satellite from these models and uploaded to each SV. The SV then transmits information relating to its position by modulating a direct sequence spread spectrum signal having a chip rate of 1.023 MHz onto a 1.5-GHz carrier.
A GPS receiver calculates its position by combining the delay or phase of the signal received from the SV, which indicates the position of the receiver relative to the SV, with information relating to the position of the SV. Because of inaccuracies in the receiver""s timebase oscillator, signals from at least four SVs are required to resolve a position in three dimensions, although signals from additional SVs (if available) may be used to provide better accuracy.
It is desirable to augment certain wireless systems for mobile communications by adding the capability to locate the position of a particular mobile unit. One reason is a regulation promulgated by the Federal Communications Commission (FCC) (Docket No. 94-102, Third Report and Order adopted Sep. 15, 1999, released Oct. 6, 1999) which requires all cellular carriers in the United States to be able to locate the position of a cellular telephone making an emergency 911 (xe2x80x98E-911xe2x80x99) call within 50 meters for 67 percent of calls and within 150 meters for 95 percent of calls by October 2001. Other uses for position location capability in wireless communications systems include value-added consumer features such as navigation and vehicle fleet management support.
In a method according to an embodiment of the invention, correction factors are transferred in a predetermined order. From this predetermined order, the particular stored or calculated values to which each correction factor relates may be identified.